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Date: 13 December 2004 Copyright: NASA Show in archive: false
The Sun is located on the left, out of the scope of the animation. As the animation begins, we see magnetic field lines (yellow lines) and arrows moving around the Earth's magnetosphere, showing how our magnetic field is naturally oriented to the north: the field flows out of the south pole and into the north.
The animation then depicts how the Interplanetary Magnetic Field (IMF) interacts with the Earth's magnetic field: first when the IMF is pointing north, then when it points south.
The IMF, carried by the solar wind, is symbolised by a red line; more precisely, only the Bz component is represented here.
When the IMF is oriented to the north (arrows pointing up), the IMF cannot connect to our magnetic field on the dayside. In this case, the solar wind flows around the magnetosphere.
But when the IMF is oriented southward (arrows pointing down), magnetic reconnection occurs as the IMF can connect to the Earth's northward magnetic field (orange field lines). The solar wind then drags the reconnected field lines from the dayside to the nightside, allowing the plasma to pour into the tail of the magnetosphere. This drag stretches the field lines, and stores the energy in the form of magnetic tension.
As the field lines pile up on the nightside, the system becomes unstable. Reconnection happens again, this time in the middle of the tail (a phenomenon associated with substorm): the newly open magnetic field lines reconnect to form closed field lines, which return back to the Earth. When this occurs, stored particles and energy are released both earthward and tailward. These phenomena energize ions and electrons, inject some of them into the ring current, and greatly increase the rate at which energy is released in the magnetosphere, which, in particular, produce auroras.
